Q: A force $ \vec{F} = (2 \hat{i} + 4 \hat{j} ) $ N displaces the body by $ \vec{s} = ( 3 \hat{j} + 5 \hat{k} ) $ m in 2 sec. Power generated will be
(a) 11 watt
(b) 6 watt
(c)22 watt
(d) 12 watt
Click to See Answer :
Ans: (b)
Sol: Power , $\displaystyle P = \vec{F}.\vec{v} $
$\displaystyle \vec{v} = \frac{\vec{s}}{t} $
$\displaystyle \vec{v} = \frac{3}{2} \hat{j} + \frac{5}{2} \hat{k} $
$\displaystyle P = (2 \hat{i} + 4 \hat{j} ) . (\frac{3}{2} \hat{j} + \frac{5}{2} \hat{k} ) $
P = 6 Watt